Totally confined explosive welding

ABSTRACT

A simple means for eliminating the noise and debris of explosive welding techniques by totally enclosing and applying the explosive pressure through the wall of the enclosure.

United States Patent [191 Bement [4 1 Mar. 19, 1974 TOTALLY CONFINEDEXPLOSIVE WELDING [75] Inventor: Laurence J. Bement, Newport News,

The United States of America as represented by the National Aeronauticsand Space Administration, Washington, DC.

Filed: Sept. 14, 1972 Appl. No.: 289,048

[73] Assignee:

US. Cl. 29/470.1 Int. Cl 323k 21/00 Field of Search..... 29/421 E,470.1, 486, 497.5

3,316,627 5/1967 Suzuki et al. 29/470.1 3,409,969 1l/l968 Simons et al.29/157.3 3,446,047 5/1969 Cleland 72/56 3,477,262 11/1969 Schmidtke etal. 72/56 3,491,798 l/l970 Beshara 138/89 3,555,656 '1/1971 Brown et a1.29/470.l X 3,566,646 3/1971 Walkup 72/56 3,590,877 7/1971 Lepoold H29/421 3,611,767 10/1971 Berman et a1. 72/56 Primary Examiner-J. SpencerOverholser Assistant Examiner-Rona1d J. Shore Attorney, Agent, orFirm-Howard J. Osborn et al.

[5 7] ABSTRACT A simple means for eliminating the noise and debris ofexplosive welding techniques by totally enclosing and applying theexplosive pressure through the wall of the enclosure. 7

5 Claims, 4 Drawing Figures il/r.

TOTALLY CONFINED EXPLOSIVE WELDING ORIGIN OF THE INVENTION The inventiondescribed herein was made by an employee of the United States Governmentand may be manufactured and used by or for the Government forGovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION This invention relates generally toexplosive welding techniques and specifically to a means of limiting thenoise and products of the explosive process.

Explosive welding as presently practiced is an efficient method forbonding materials which are difficult to weld by more conventionalmeans. It is particularly useful for thin materials which might sufferdamage or change properties due to heat; for specific materials such astitanium or aluminum which have unique properties requiring a highdegree of skill for conventional welds; and for large structures whichrequire complex and expensive equipment to obtain uniform welds byconventional means.

Explosive welding is a comparatively simple procedure with which suchmaterials may be bonded by relatively unskilled personnel. In such atechnique the parts to be welded are spaced slightly apart byseparators, jigs, or dimples and explosive is attached to one of thepartsdirectly opposite the proposed bond area. The other part to bewelded is rigidly supported on an anvil or table. Upon detonation of theexplosive the parts to be welded are driven together with such forcethat they are metallurgically bonded. It is generally accepted that asthe collision occurs remaining surface contaminants are stripped away,providing virgin metal for the metallurgical bond.

The tooling requirements for such an operation are very minimal.Satisfactory seam welds can be secured with only a cord-like preformedexplosive, aluminum spacers, clamps, masking ,tape and a commerciallyavailableblasting cap detonator. The fabrication designer is able tospecify all these items so that an unskilled person can performtheoperation with reasonable certainty that a leak-proof bond will result.Because. of the minimal tooling, low cost, and ability to weld aluminumand titanium, application of the explosive welding technique isanticipated in the aircraftindustry and in extra-terrestrialapplications. It is viewed as particularly applicable to the fabricationof space stations in orbit. Despite its advantages and the fact that thetechnique has been under development for almost twenty years, it hasseen relatively little industrial use. I I v This may be because of thepsychological effects of the noise and scattering of debris from theexplosion. While such phenomena are relatively minor when a small amountof explosive is used, they do present some safety hazard and create areluctance to the use of this otherwisevaluable technique. This sameexplosive debris presents another problem in some applications. In highvacuum, space and other applications which require close control.ofpotential contaminants, the explosive welding technique presents theproblem of scattering debris into areas where it causes undesirablecontamination. The present invention solves these problems withoutadding significantly to the complexity or cost of the basic technique.

SUMMARY OF THE INVENTION The present invention is a method andassociated apparatus for confining the undesirable byproducts andlimiting the noise of explosive welding, the use of which has beenlimited because of such phenomena. The apparatus is comprised of asimple enclosure into which the explosive is placed and within which theexplosive is placed and within which the explosion occurs. Due to theshape of the enclosure, the placement of the explosive within it, andthe manner in which the enclosure is placed upon the material to bewelded, the force of the explosion is transmitted to the proposed bondarea. Moreover, since the explosion is totally confined within theenclosure the noise of the explosion is reduced dramatically and nodebris is strewn about to contaminate the weld area or create personnelhazards.

.In one example of a seam bonded by explosive welding,

flattened steel tubing is used as an enclosure. This is attached to theweld material by the use of masking tape, just as the explosive itselfis attached in unconfined explosive welding. The preformed explosive isslipped into the tubing along with a strip of silicone rubber whichholds the explosive against the flattened side of the tubing which isadjacent to the proposed weld area. The explosion is initiatedelectrically by a commercially available detonator which threads into afitting welded to one end of the tubing. The noise generated is no morethan the rattle of metal, whereas an unconfined explosion creates noisecomparable to that of a very close shotgun firing. The residue fromunconfined explosive welding contains carbon, portions of the explosivesheathing material, and masking tape. Such residue is completelycontained when the confined technique is used so that the use of such abonding method becomes practical even in the restricted environment of aspace station.

The method of confined explosive bonding retains all the benefits of theoriginal technique. It is capable of welding methods that are normallyextremely difficult; it can weld very thin materials'such as those usedon aircraft and spacecraft; it requires very little tooling so that itmay be used in remote installations by unskilled labor. Because of theseoriginal benefits, the totally confined explosive welding methodeliminates the major remaining problems involved in the process, thoseof noise and debris, with no significant sacrifice of simplicity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of theapparatus for confining the explosive showing a typical cross section;

FIG. 2 is an axial cross-sectional view of the detonator adapterassembly;

FIG. 3 is an end view of the detonator adapter assembly; and

FIG. 4 is an axial cross-sectional view of the closed end fitting.

DETAILED DESCRIPTION OF THE INVENTION The embodiment of the inventionselected for illustration as shown in FIGS. 1 and 2 is one used for seamwelding. FIG. 1 shows a typical cross-sectional view perpendicular tothe planes of sheet materials 12' and 14 to be welded and to thecenterline of the proposed bond area at which they will be joined. Uppersheet 14 is 0.040 inch thick aluminum; and while lower sheet 12 is 0.25inch aluminum in this example, it should be understood that thesematerials may be either the same or different thicknesses. Lower sheet12 is placed upon anvil 11 which supports the work, furnishes reactiveforce during the explosion, and absorbs excess shock waves. Separators13 made of aluminum 0.010 inch thick, are placed on either side ofproposed bond area 10 and are located with sufficient clearance so thatthey will not interfere with the subsequent bonding. Separation isrequired in the explosive welding process so that a velocity may beimparted to one or both of the pieces to be welded. This velocity is abasic requirement for the explosive welding process so that thecollision between the workpieces strips the mating surfaces clean andmetallurgically bonds them together. In the arrangement shown in FIG. 1,the velocity is imparted to upper sheet material 14 by the forcegenerated by the detonation of explosive 17. This force is transmittedthrough the wall of the steel tubing of enclosure 16 and the siliconegrease 15 which is placed between the lower flattened side of tubing 16and the upper surface of the material to be bonded 14. Grease 15 is usedto assure that no voids exist between tubing 16 and workpiece 14 andthat the explosive pressure is efficiently transmitted to the materialto be welded. Explosive 17 is completely contained within steel tubing16 and its appropriate end fittings. This containment prevents anyproducts of the explosion from reaching the surrounding environment andvirtually eliminates the noise of the explosion. Enclosure 16 used inthe arrangement shown in FIG. 1, is a steel tubing and may be formedfrom type 347 alloy. It is 0.85 inch on the longest dimension of itscross section and is 0.30 inch high. The wall thickness is 0.030 inchand the dimension of the flat surface is 0.5 inch. Enclosure 16 isattached to upper sheet 14 by the use of strips 19 of conventionalmasking tape.

Explosive 17 used in the specific embodiment shown is a linear ribbonconstructed oflead sheathed RDX explosive. It is available withexplosive loads of 7 to 25 grains per foot but in the specific example15 grains per foot is used. Its size is 0.025 inch thick by 0.315 inchwide overall. It may safely be cut to length with a scissors. The use ofan enclosure to contain the byproducts of the explosion and reduce noiseis in no way limited to either the specific explosive or the specificenclosure described herein. However, it should be understood that theenclosure must be selected to contain the explosion without rupturewhile the explosive shouldbe selected with consideration of materialsand thicknesses to be welded.

The silicone filler strip 18 is slipped into steel tubing 16 along theexplosive 17. Together they are sized to form a snug but not tight fitwithin tubing 16. Filler strip 18 holds explosive 17 in contact with theflattened side of steel tubing 16 during preparation. When the explosionoccurs filler strip 18 attenuates and diffuses that force which isdirected away from weld area 10 so that no rupture occurs in the topsideof tubing 16. The silicone rubber filler strip 18 also contributes tothe reduction of the noise from the operation.

FIGS. 2 and 3 illustrate the detonator adapter assembly which is used inconjunction with the configuration of FIG. 1 to accomplish totalenclosure of the explosive. Because of the shock pressures generated bythe explosion such fittings must be structurally strong and containpressure seals at all joints. This is accomplished in the illustratedassembly by attaching steel enclosure tube 16 to steel end housing 21 atweld joint 22 by welding prior to setting up the explosive weldingoperation. The commercially available detonator cartridge 26 is screwedinto end housing 21 by means of threads 27 and tightened against O-ring28 to complete the pressure seal to the interior of the explosiveenclosure extension 31 drilled into the center of housing 21.

The aluminum restraining adapters 23 and 24 are added to the assembly toprevent the explosive shock from fracturing enclosure tube 16 at weldjoint 22. The explosion is initiated by supplying current to electricalpins 29 which detonates charge 30, in turn detonating explosive 17. Theexplosive detonates along its length at a finite velocity of the orderof 26,000 ft/sec. As this detonation wave passes weld joint 22 betweenend housing 21 and tubing 16 the stress created by the shock wave on theunsupported tubing would be such as to rupture the tubing at the weld.Upper restraining adapter 23 is attached to end housing 21 by bolt 32,while lower restraining adapter 24 is attached to end housing 21 by bolt33. Together the restraining adapters 23 and 24 completely surroundtubing 16 and support it in all directions. This support decreases asthe distance from the end housing increases because of the taperedconstruction of the restraining adapters. Upper restraining adapter 23provides restraint which at end housing 21 approaches the same degree ofrestraint afforded by the end housing while at the other end the adapteris tapered to approach the strength of only the unsupported tubing 16.Lower restraining adapter 24 furnishes restraint approaching that of theend housing at one end, but is tapered such that at the other end itapproximates the restraint provided to tubing 16 by the work piece 14.The surface of the tubing 16 against which explosive l7 acts, in thisexample the lower surface, must be supported in some manner for theentire length of the explosive in order to prevent a discontinuity atthe work piece which would accentuate the stress on the tubing and causerupture. The upper surface of the tubing does not require such backingsince the shock from the explosive is damped by the silicone rubberfiller material 18 and there is no backing material along the totaltubing length.

FIG. 4 shows the closed end fitting used at the end of the tubingopposite from the detonator. It comprises a simple end cap 36 drilled tofit outside tubing 16. The tubing is inserted into cap 36 and welded at35. Tubing l6 rests on support 37 for its length not supported by theweld pieces to meet the requirements for shock restraint. However, whentubing 16 is made long enough in the section that contains no explosive17, the shock wave is reduced to a level that requires no support. Sucha modification is valuable where the welding is done in confinedquarters and it is desirable to place the end fitting elsewhere.

While the benefits of explosive welding are most apparent in longseamwelding, neither the prior technique nor the invention described hereinis limited to such a configuration. Any operation which previously usedexplosive welding can benefit from the enclosing of the explosive so asto limit the noise and debris. In spotwelding, as another example, smallcontainers can be constructed which enclose the charge used for eachspot.

Another variation of the technique prescribed by this invention is theuse of two enclosures to contain the dual explosive charge used when asecond charge is substituted for anvil 11 in the prior example. Theconsive pressure to the bond area through the walls of the enclosure,said enclosure containing the explosion without rupture.

2. In the confined explosive welding method as in finement technique isalso effective in its simplest form 5 claim 1 filling the voids betweenthe explosive enclowhen no silicone grease as shown by 15 in FIG. 1 isused. In such an option only a slight loss of efficiency of transmissionof explosive force may be experienced if the surfaces of tubing 16 andworkpiece 14 do not mate exactly. The silicon rubber filler material 18provides for other variations. In one case, it may be entirely removedand the absence of attenuation of the explosive force counteracted bystrengthening the enclosure, shaping the enclosure, or minimizing thecharge of explosive. The filler material may also be shaped and made ofa material such that it will actually reflect the force back in thedirection of the bond thereby increasing the force available from agiven charge. Such a variation is shown in FIG. 3 in which fillermaterial 38 has a triangular undercut 39. The enclosure may likewisebe'constructed so as to deflect the forces back to the work area toaccomplish a similar increase in effective'force.

It is to be understood that the forms of the invention herein shown aremerely preferred embodiments. Various changesmay be made in shape, sizeand the arrangement of parts; equivalent means may be substituted forthose illustrated and described; and certain features may be usedindependently from other features without departing from the spirit andscope of the invention as defined in the following claims. For example,the enclosure shown is constructed from flattened steel tubing. Other.shapes and materials may be used where the parts to be welded and theexplosive used make them more effective or economical.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In bonding materials by explosive welding means wherein noise anddebris from the explosion may cause disturbance to personnel or damageto property, the improved method which comprises:

totally enclosing the explosive material within a sealed enclosure todimish noise and contain the products of the explosion;

attaching the enclosure to the material to be bonded;

detonating the explosive material within the enclosure; andaccomplishing the bond by the application of explosure and the materialto be bonded with a substance which transmits the explosive pressure tothe bonding area.

3. In the confined explosive welding method as in claim 1 filling thebalance of the explosive enclosure with a material which attenuates anddiffuses the explosive pressure which is not directed toward the bondarea.

4. In the confined explosive welding method as in claim 1 filling thebalance of the explosive enclosure with a shaped material whichconcentrates the explosive pressure upon the bond area.

5. In bonding material by explosive welding, an improved method of totalconfinement as in claim 1 whereby noise and debris are limited which iscomprised of the steps of:

providing a complete enclosure of flattened steel tubing with endfittings which seal off the ends of the tubing;

inserting a ribbon-shaped explosive into the enclosure in such a mannerthat a flat side of the ribbon explosive rests against an inside flatwall of the enclosure;

inserting a resilient filler strip between the explosive ribbon and theopposite wall of the enclosure whereby the ribbon explosive is heldfirmly against the enclosure wall;

providing the materials to be bonded;

applying a void filling substance to one material to be bonded;

attaching the enclosure to the material to be bonded whereby the outersurface of the enclosure wall against which the explosive ribbon restsis held against the material to be bonded and compresses thevoid-filling substance;

detonating the explosive within the enclosure;

bonding the materials by application of explosive pressure to the bondarea through the flat wall of the enclosure and the void-fillingsubstance; and

removing the unruptured enclosure from the bond

1. In bonding materials by explosive welding means wherein noise anddebris from the explosion may cause disturbance to personnel or damageto property, the improved method which comprises: totally enclosing theexplosive material within a sealed enclosure to dimish noise and containthe products of the explosion; attaching the enclosure to the materialto be bonded; detonating the explosive material within the enclosure;and accomplishing the bond by the application of explosive pressure tothe bond area through the walls of the enclosure, said enclosurecontaining the explosion without rupture.
 2. In the confined explosivewelding method as in claim 1 filling the voids between the explosiveenclosure and the material to be bonded with a substance which transmitsthe explosive pressure to the bonding area.
 3. In the confined explosivewelding method as in claim 1 filling the balance of the explosiveenclosure with a material which attenuates and diffuses the explosivepressure which is not directed toward the bond area.
 4. In the confinedexplosive welding method as in claim 1 filling the balance of theexplosive enclosure with a shaped material which concentrates theexplosive pressure upon the bond area.
 5. In bonding material byexplosive welding, an improved method of total confinement as in claim 1whereby noise and debris are limited which is comprised of the steps of:providing a complete enclosure of flattened steel tubing with endfittings which seal off the ends of the tubing; inserting aribbon-shaped explosive into the enclosure in such a manner that a flatside of the ribbon explosive rests against an inside flat wall of theenclosure; inserting a resilient filler strip between the explosiveribbon and the opposite wall of the enclosure whereby the ribbonexplosive is held firmly against the enclosure wall; providing thematerials to be bonded; applying a void filling substance to onematerial to be bonded; attaching the enclosure to the material to bebonded whereby the outer surface of the enclosure wall against which theexplosive ribbon rests is held against the material to be bonded andcompresses the void-filling substance; detonating the explosive withinthe enclosure; bonding the materials by application of explosivepressure to the bond area through the flat wall of the enclosure and thevoid-filling substance; and removing the unruptured enclosure from thebond area.